A probe over ExxonMobil’s apparent cover-up of climate change risks has expanded. Now 17 states’ US attorneys general have joined New York’s investigation and vowed more probes into fossil fuel firms.

US attorneys general are going to cooperate in order to investigate whether fossil fuel companies have misled investors on climate change and global warming issues by perusing their financial interests.

“We have heard the scientists and we have heard what is happening to the planet,” said New York attorney general Eric Schneiderman at a briefing for reporters. “Every fossil fuel company has a responsibility to be honest with its investors.”

It has been nearly five months since Schneiderman launched an investigation into whether ExxonMobil, the largest US gas and oil company, had misled the public and investors about the risks of climate change. His actions were followed by a similar inquiry that had been opened in California earlier this year.

The multi-state effort has now been joined by attorneys general from Connecticut, Colorado, Maryland, Massachusetts, Virginia, and the US Virgin Islands along with another 11 states as a part of an unprecedented “AGs United for Clean Power”group.

The “first-of-its-kind coalition” as described by former Vice President Al Gore would be working to “fight for climate progress.”

All of the joining members previously formed coalition of 25 states, cities and counties led by Schneiderman, which defended President Obama’s Environmental Protection Agency’s (EPA) “Clean Power Plan” against a legal challenge.

New York, Massachusetts, California and the US Virgin Islands have started investigations already.

"If Exxon Mobil has tried to cloud their judgment, we are determined to hold the company accountable,” Virgin Islands Attorney General Claude Earl Walker said during the Tuesday news conference in New York.

Attorney General Maura Healey of Massachusetts also went on to announce her state’s willingness to join the effort, stressing the severity of the climate change problem.

“It’s incredibly serious when you think about the human and economic consequences,” Healey said.

Fossil fuel companies that deceived must be held accountable. That's why we too have joined in investigating Exxon.

Although none of the other officials were present, aside from Healey and Walker who announced inquiries of their own, Schneiderman said, “not every investigation gets announced at the outset.”

“If there are companies, whether they’re utilities, whether they’re fossil fuel companies, committing fraud in an effort to maximize their short-term profits at the expense of the people we represent, we want to find out about it. We want to expose it and want to pursue them to the fullest extent of the law,” the New York attorney general said.

Gore, an active climate policy advocate, joined the attorneys general at the announcement, calling the coalition a “key step on the path to a sustainable, clean-energy future.”

"We cannot continue to allow the fossil fuel industry or any industry to treat our atmosphere like an open sewer or mislead the public about the impact they have on the health of our people and the health of our planet,” Gore said.